Introduction

Cneoglossidae, monogeneric to Cneoglossa Guérin-Méneville, 1849, a Neotropical genus with nine known species distributed from Mexico to Brazil (Rio Grande do Sul), is represented by very small beetles (3-5 mm in length) with soft integument, dark elytra, and a bicolored pronotum concealing partially the head when seen from above (Costa et al., 1999, 2005).

Adults are usually attracted to lights at night. The only known larvae of Cneoglossa (C. edsoni) were collected in a small shallow stream, with moderate to fast running water and muddy or sandy bottoms, depending on the declivity of hill sides. The water was clear and slightly acidic (pH 6.0-6.2). The cneoglossid larvae were found inside submerged rooting brushwood, together with some larvae of Lutrochidae (Lutrochus germari Grouvelle, 1889) and Elmidae (Macrelmis sp.) (Costa et al., 1999).

Abdomen with five visible ventrites; the first 3 of which connate but separate by distinct sutures; 1st ventrite deeply excavate for reception of metacoxae, without intercoxal process. Male 9th tergite entire; 9th and 10th tergites not fused. Female 8th sternite with spiculum ventrale, with 1-paired projection.

Pupae

Adecticous, exarate, without gin-traps.

Taxonomy

Guérin-Méneville (1843) included Cneoglossa within the Dascillidae, but this is a nomen nudum, since C. collaris (type-species of Cneoglossa) was formally described by him only in 1849. Champion (1897) sustained the systematic position and erected the tribe Cneoglossini. Crowson (1972) transferred it to the Cantharoidea, including it in his new family Cneoglossidae. Lawrence (1982) followed Crowson’s (l. c.) ideas, but latter (1988) he included it in his Psephenoidea (Psephenidae, Callirhipidae, Eulichadidae, Cneoglossidae, Ptilodactylidae and Chelonariidae). Lawrence & Britton (1991) transferred Cneoglossidae to Byrrhoidea plus Psephenoidea of Lawrence (1988).

Relationships of Cneoglossidae to Other Beetles

Lawrence et al. (1995) presented a cladistic analysis of the Elateriformia plus Scirtoidea. The authors considered Psephenidae as the sister group of Cneoglossidae, including both in their expanded Byrrhoidea. Lawrence & Newton (1995) placed Cneoglossidae within Byrrhoidea, suggesting a position near Ptilodactylidae or Psephenidae. Beutel (1995), in a cladistic analysis of Elateriformia based only on morphological structures of immatures stages, emphasized the characters transformation of the head which according to him play a predominant role in the evolution, but did not present a new classification of that series.

Costa et al. (1999) in a cladistics analysis of Byrrhoidea pointed out a sister-group relationship between Cneoglossidae and Psephenidae supported by the presence, in adults, of paired glandular openings on abdominal tergites. The same sister-group relationship was evidenced by Lawrence et al. (1995).

Larvae of Cneoglossa (C. edsoni) are very similar to larvae of species of Anchytarsinae and Epilichinae (Ptylodactylidae). However, according to the cladistic analyses conducted by Costa et al. (1999), this resemblance (v.g. presence of paired pygopodium with apical hooks and osmoregulatory organs) is interpreted as the result of homoplasies shared by aquatic larvae of distinct and independent lineages, subject to convergent adaptations to life in fast running waters.

About This Page

We thank Ricardo P. Vanin for the electronic treatment of figures of larvae and pupae. To Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the Research Grant 302721/2007 – 0 to C. Costa.

Page: Tree of Life
Cneoglossidae. Cneoglossa.
Authored by
Cleide Costa and Sergio Antonio Vanin.
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